The present invention pertains to lathes, and more particularly to chucks and other holding assemblies which can be installed on a lathe to hold a workpiece. A typical chuck comprises a plurality of circumferentially spaced jaws which can be moved radially inwardly and outwardly to grip a workpiece, such as a shaft, by its side surfaces. Other types of holding assemblies are known. For example, some assemblies include face-driver or stab-type formations which frictionally engage the axially facing end of a workpiece. These formations may be sharp chisel points which "bite into" the end of the workpiece, or they may be adapted to mate with pre-formed depressions in the end of the workpiece. In any event, either the chuck or the stab-type assembly may be installed interchangeably on the headstock of the lathe.
Several problems are associated with the use of such conventional holding assemblies. These may be illustrated by describing the process of turning the outer diameter, hereafter "O.D.," of a shaft to a desired finished dimension. There are several ways of accomplishing this using conventional tools of the types described above, but none are entirely satisfactory.
In one typical procedure, a chuck is installed in the lathe, and a workpiece is held near one end by the chuck while the portion of the workpiece adjacent its opposite end is rough cut to near finished diameter. It is not possible to advance the cutting tool along the entire length of the workpiece while one end thereof is held in the chuck. Thus, the workpiece must be removed and reversed in the lathe so that the chuck holds the workpiece by that end which has already been rough cut while the other end (original holding end) is cut.
Next, a fine finishing cut is made, with a different cutting tool, to smoothly finish the O.D. of the workpiece and reduce it to the desired final dimension. Again, because the cutting tool cannot move past the chuck jaws, the fnishing cut must be made in two sections, one beginning from each end of the workpiece, the workpiece being reversed in the lathe after the first section is cut. This can leave scar, step or slight offsetting of diameter at the juncture of the two sections, and this is undesirable, or even unacceptable, for some applications.
Accordingly, another common procedure is to cut the original workpiece longer than the desired finished shaft length, finish the O.D. in a single pass stopping short of the chuck, and then remove and discard the end of the workpiece which was held by the chuck during the finishing cut. This alternative method is time-consuming and wasteful.
Any attempt to perform an entire cut in a single pass with the chuck removed and the workpiece held only by a face-driver or stab-type holding assembly would probably be unsuccessful, or at least unreliable, in many instances, especially when the cutting tool is working distal the headstock, due to high torque.
Still other problems revolve around the fact that conventional chucks and stab-type holders are completely separate and distinct assemblies which must be interchanged on the lathe. Obviously, this results in delays and inconvenience.